Common focusing electrode for plurality of beams and having same plurality of internal shields

ABSTRACT

An improvement is provided in a multibeam bipotential electron gun structure for use in a cathode ray tube whereby the electrostatic focus lensing effected by the focus and accelerating electrodes is beneficially improved. The invention relates to a tube-like encompassing member that is formed integral with each of the front apertures in the focus electrode, such being fabricated in a manner to extend rearward toward a related rear aperture in the same electrode thereby effecting shielding for the respective electron beam traversing the region. This shielding provides improved symmetry of the equipotential lines of force comprising the field of the focus lensing in particularly the region of low beam velocity within the focus electrode portion of the lensing field, thereby providing a welldefined beam spot landing at the screen.

United States Patent [19] Say et al.

[ June 17, 1975 [75] Inventors: Donald L. Say, Waterloo; Harry E.

Smithgall, Seneca Falls, both of N.Y.

[73] Assignee: GTE Sylvania Incorporated,

Stamford, Conn.

3,772,554 ll/l973 Hughes ..3l3/4l4X Primary ExaminerRobert SegalAttorney, Agent, or FirmNorman J. OMalley; Frederick H. Rinn; Cyril AIKrenzer [57] ABSTRACT An improvement is provided in a multibeambipotential electron gun structure for use in a cathode ray tube wherebythe electrostatic focus lensing effected by the focus and acceleratingelectrodes is beneficially improved. The invention relates to atube-like encompassing member that is formed integral with each of thefront apertures in the focus electrode, such being fabricated in amanner to extend rearward toward a related rear aperture in the sameelectrode thereby effecting shielding for the respective electron beamtraversing the region. This shielding provides improved symmetry of theequipotential lines of force comprising the field of the focus lensingin particularly the region of low beam velocity within the focuselectrode portion of the lensing field, thereby providing a welldefinedbeam spot landing at the screen.

4 Claims, 7 Drawing Figures 1 COMMON FOCUSING ELECTRODE FOR PLURALITY OFBEAMS AND HAVING SAME PLURALITY OF INTERNAL SHIELDS BACKGROUND OF THEINVENTION This invention relates to a plural beam cathode ray tube andmore particularly to a multibeam bipotential electron gun structureemployed in a color cathode ray tube construction.

Many cathode ray tubes currently utilized in color televisionapplications are of the type employing a patterned multiphosphorcathodoluminescent screen interiorly disposed on the viewing panel ofthe envelope wherein an apertured or multiopening mask is spatiallypositioned relative thereto. A plurality of electron beams, emanatingfrom an electron gun mount structure positioned within the envelope, aredirected to converge at and traverse the apertured mask to discretelyimpinge and luminescently excite the electronresponsive phosphors of thescreen therebeyond. Focusing of the individual electron beams isconventionally achieved by means of bi-potential lensing. This type offocus lensing is dependent on the ratio of the focus voltage to therespective accelerating electrode or anode voltage. For example, inbi-potential focusing, the potential applied to the focus electrode isin the order of to percent of the anode voltage, thus with an anodevoltage in excess of 20,000 volts, the focus voltage is usually wellabove 3,000 volts. With the advent of smaller and more compact multibeamelectron gun structures, unitized focusing and accelerating electrodeshave been developed wherein the plurality of beams share portions of therespective single electrodes. The unitized focusing electrode is acommon structure having, for example, three spaced-apart apertures in acommon plane therein, one for each of the beams traversing theelectrode. The associated accelerating electrode is also a commonstructure having a like number of related apertures therein. These twoelectrodes are positioned adjacent to one another in a substantiallylongitudinal manner to form focusing lenses for the respective electronbeams traversing these electrodes. In some gun constructions, theapertures in the accelerating electrode are offset slightly from thosein the related focusing electrode to form an eccentric lens. This typeof offset lens is beneficial in that it not only focuses an electronbeam but also initiates a desired slight deflection of the beam toward aconvergent position relative to the two other related beams emanatingfrom the gun structure. While advantageously initiating the desiredconvergence, it has been found that the offset focusing lens evidences apartial nonsymmetrical field which influences the beam to effect anoticeably distorted spot image at the screen.

OBJECTS AND SUMMARY OF THE INVENTION It is an object of the invention toreduce the aforementioned disadvantages by improving the multibeambipotential electron gun structure in a manner to achieve improved fieldsymmetry of the focus lensing for each of the electron beams emanatingtherefrom.

It is another object of the invention to provide an improvement in acathode ray tube multibeam bipotential electron gun structure whereofthe beams projected therefrom are focused on the screen as spots free ofastigmatic distortions.

These and other objects and advantages are achieved in one aspect of theinvention by an improvement in the multibeam bipotential electron gunstructure of the cathode ray tube. For example, in a three beam electrongun structure, focusing of the individual beams is accomplished bylensing effected by the focusing and accelerating electrode members. Thefocusing electrode is a common member having three from and rearspatially related apertures therein. Each of the front apertures has atube-like encompassing member formed integral therewith and fabricatedin a manner to extend rearward toward a related smaller-dimensioned rearaperture, thereby effecting shielding for the respective electron beampassing therethrough. A common accelerating electrode member isadjacently positioned ahead of the focusing electrode. This acceleratingelectrode has three spaced-apart apertures located therein whichsubstantially mate with the front apertures of the focusing electrodemember. At least two of the accelerating electrode apertures areeccentrically aligned relative to the related focusing electrode frontapertures to form therebetween offset electrostatic lensings forfocusing the respective individual electron beams trave rsing thatparticular region. Each of the focusing electrode shielding membersprovides a marked enhancement of beam focusing by effecting improvedsymmetry of the equipotential lines of force in particularly the regionof low beam velocity in the focusing electrode portion of theelectrostatic lensing field. The improved symmetry of the focus lensinginfluences the shaping of the beam passing therethrough to provide asubstantially small and well-defined beam spot landing at the screen.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. I is a sectional view of thecolor cathode ray tube illustrating componental portions thereof;

FIG. 2 is an enlarged partially sectioned view of a multibeam electrongun structure wherein the invention is shown;

FIG. 3 is a slightly enlarged plan view illustrating the forward portionof the grid three electrode member taken along the line 33 of FIG. 2',

FIG. 4 is a prior art illustration delineating an enlarged sectionalview showing the relationship of a single focusing electrode aperture toa single accelerating electrode aperture whereof the equipotential linesof the non-symmetrical offset lensing field are indicated;

FIG. 5 is a sectional view showing a single accelerating electrodeaperture related to a single focusing electrode aperture incorporatingthe invention wherein the modified symmetrical lensing field isindicated;

FIG. 6 is a partial sectional view of an inline multibeam electron gunshowing the focusing electrode and the accelerating electroderelationship with the invention delineated in the focusing electrodemember; and

FIG. 7 is a plan view illustrating the forward portion of the commoninline focusing electrode member taken along the line 77 of FIG. 6.

DESCRIPTION OF THE PREFERRED EMBODIMENTS For a better understanding ofthe present invention, together with other and further objects,advantages and capabilities thereof, reference is made to the followingspecification and appended claims in connection with the aforedescribeddrawings.

With reference to the drawings, there is illustrated in FIG. 1 apartially sectioned multibeamed color cathode ray tube 11 having anencompassing envelope comprised of an integration of a neck portion 13,a funnel portion 15, and a face or viewing panel portion 17. A patternedscreen 19 including a repetitive plurality of color-emitting phosphorcomponents is suitably disposed on the interior surface of the viewingpanel 17. A multi-opening mask member 21 is positioned within theviewing panel, by means not shown, in a manner whereof the multi-openingportion 23 is spatially related to the patterned screen 19. Extendinginto the neck portion 13 is a skirt of a high voltage internalconductive coating 25 which is a continuation of the coating coveringthe interior surface of the funnel portion 15 of the tube envelope.Positionally encompassed within the neck portion is a multibeambipotential electron gun structure 27 having a longitudinal axis 29therethrough. Two of the plurality of individual electron beams 31 and33 are shown emanating from the gun structure, whereupon they areconvergently directed toward the patterned screen 19. Mounted exteriorlyupon the envelope, in substantially the neckfunnel transition region 35,is a yoke 37 or deflection coil arrangement which is formed andenergized to impart scanning motion to the referenced electron beams 31and 33. Positioned behind the yoke means, on the exterior of the neckportion 13 of the envelope, are magnet means 39 and 41 of the dynamicconvergence device, two of which are shown. The magnetic fieldsemanating from the respective magnet means effect converging influenceson the respective beams as they traverse the convergence cage 43attached to the forward end of the multi-beamed electron gun structure27.

For greater exposition, reference is directed to FIGS. 2 and 3 whereinthe improved multi-beam bipotential electron gun structure 27,incorporating an embodiment of the invention, is exemplarily illustratedas a three-beam delta arrangement whereof the respective beams arepositioned in a substantially equispaced offaxis orientation. In amultibeam gun structure, each of the respective beams traverses asubstantially longitudinal arrangement of several functionally relatedelectrode members embodying, as for example, apertured grid electrodesone through four positioned in sequential orientation from a relatedcathode or electron generating component. These several electrodemembers are positionally held in spaced relationship with respect toeach other by a plurality of insulative support rods 45, of which twoare shown. In greater detail, a single or central ray of an exemplaryelectron beam 33 is shown as emanating from the electron-emissivethermionic cathode 47, whereupon the beam is initially shaped andinfluenced by the apertured individual grid one control electrode 49 andthence directed through the apertured grid two or screen electrode 51.The travelling beam then enters one of the rear apertures 53 formed inthe rear aperture plane 55 of the composite common grid three focuselectrode member 57, and proceeds therethrough leaving by a largeraperture 59 formed in the front aperture plane 61 of that member;whereupon the beam enters a related aperture 63 in the common grid fouraccelerating electrode 65 to which is terminally attached theaforementioned convergence cage assembly 43. g

The unitizdf'focuselectrode 57, of delta beam arrangement, isillustrated as being fabricated of two substantially cupshaped members67 and 69 which are suitably integrated by peripherally applied bondingat the respectively mated flanges 71 and 73. FIG. 3 presents a viewlooking into the forward member 69 from the flange 73. As shown,discretely configurated portions of the peripheral flange are typicallyembedded in the spaced-apart support rods 45 to provide rigid positionalsupport for the electrode member in the composite gun structure 27.

The invention relates to an improvement in the common grid three focuselectrode structure 73, wherein each of the front apertures 59 in thefront aperture plane 61 is, for example, substantially circular in shapeand has a tube-like encompassing member 77 integral with the frontaperture plane, such member being formed in a manner to extend rearwardtherefrom toward the related smaller-dimensioned rear aperture 53oriented in the rear aperture plane 55 of that electrode member. Thus,each tube-like member 77 effects shielding for the respective electronbeams passing therethrough. These shielding means are substantiallysimilar for the several beams concerned. For example, they are usuallyof substantially equal internal crosssectional dimensionings, and arepreferably substantially cylindrical in shape.

The aperture plane 64 of the grid four accelerating electrode member 65has a plurality of spaced apertures 63 therein which are of dimensionssubstantially larger than the spatially related front-oriented apertures59 in the grid three electrode member 57. At least two of thelarger-dimensioned grid four apertures 63 are eccentrically alignedrelative to the related smallerdimensioned grid three front apertures59, to form offset non-symmetrical electrostatic lenses for focusing therespective electron beams traversing the respective region.

In referring particularly to FIG. 3, the offset relationship of theapertures 59 and 63, pertaining to the focus lensing, is illustrated,for example, for one set of apertures as being substantially in radialorientation 0 with reference to the gun axis 29, whereby the peripheryof the accelerating electrode aperture 63 is phantomed to indicate itsdistal eccentricity D to the periphery of the focus electrode aperture59. The opposed peripheral portions of the two radially orientedapertures that are proximal P to the gun axis 29 are substantially matedin longitudinal alignment. The offset lensing so effected, not onlyfocuses the electron beam, but also initiates a beneficial deflectiveinfluence which imparts a slight convergent attitude to the beam withrespect to the two other beams formed in the gun structure.

For a functional explanation of the invention, attention is directed toFIGS. 4 and 5 wherein lensings affecting the focusing and trajectoriesof the beams are portrayed. FIG. 4 is an enlarged portional art viewillustrating a single grid three aperture in relationship to a spatiallyrelated single grid four aperture whereof an offset or eccentricfocusing lens is effected. The grid four accelerating electrode 65',sometimes referenced as an anode, has a relatively high anode voltage,for example, the potential may be in excess of 20 kv. The related gridthree focusing electrode 57 has a lower potential applied thereto which,for example, may be in the order of 4 to 5 kv. Both apertures 59' and63' in the prior art structures are defined by relatively short or smallre-entrant lips. The apertural interaction of the diverse gridthree-grid four potentials effects an electrostatic focusing lenswhereof the equipotential lines 79 in particularly the low voltage gridthree electrode 57' region are non-symmetrically oriented. The focusingof the electron beam 33' traversing this lensing is detrimentallyinfluenced by astigmatism or distortion introduced by thisnonsymmetrical field. For example, the near presence of the wall 81 ofthe focus electrode 57' and the short re-entry lips 83 surrounding theaperture 59' are contributory to allowing the equipotential lines 79',especially in the low-voltage region, to loop back of the aperture in anomsymmetrical manner. This displacement of the lensing field within thefocus grid produces a detrimental uncontrolled bending or astigmaticinfluence on the beam in a region of low velocity whereat the electronsare easily deflected. Such action aggravates beam spot distortion at thescreen. The beneficial aspects of the invention are illustrated in FIG.5, which is an enlarged portional view, wherein the grid three aperture59 is shown as being formed to have an integral tube-like encompassingor shielding member 77 extending rearward therefrom into the volume ofthe focus electrode structure 57. It is preferable for the shieldingmember to have a length 2 at least equally 50 percent of the radius r ofthe aperture 59 or of the resultant like dimensioned lens: e Z 0.50 r.Such longitudinal definitive shielding effects substantially symmetricalshapings of the equipotential lines of force in the low voltage portionof the lensing field, substantially within the critical portion of thefocus electrode member, thereby providing enhanced beam spot focusing atthe screen that is free of astigmatic distortion.

The invention is also applicable to a multibeam inline electron gunstructure, of which a portional sectioned region embodying the focus andaccelerating electrodes 89 and 91 is illustrated in FIGS. 6 and 7. Inthis type of gun construction, the related electrode components forcontrolling each of the respective beams are positioned in asubstantially longitudinal manner, on a substantially common plane, toprovide a center onaxis beam 93 with related beams 95 and 97 equi-spacedon either side thereof; the center rays of the respective beams beingindicated in the FIGS. 6 and 7. At least the side-related electrodearrangements include focus electrode apertures 99 having tube-likeshielding members 101 that are of substantially equal lengths. Thesideoriented accelerating electrode apertures 103 are usually offsetrelative to the corresponding focus electrode apertures 99 to providethe benefits of eccentric lensing. Such offset orientation is indicatedin phantom in FIG. 7, which presents a view looking into the forwardmember 105 of the two-piece focus electrode 89 from the plane of theflange 107. Configurated portions of the peripheral flange are suitablyembedded in the longitudinal support rod members 45' to provide rigidpositional support for the common inline focusing electrode inconjunction with the associated electrodes comprising the compositeelectron gun structure 87.

Thus, there is provided an improvement in a cathode ray tube multibeambipotential electron gun structure, wherein shielding is included in thecommon focus grid electrode in a manner to effect improved symmetry ofthe equipotential lines of force comprising the electrostatic focuslensing to provide welldefined beam spot landings on the screen.

While there has been shown and described what are at present consideredthe preferred embodiments of the invention, it will be obvious to thoseskilled in the art that various changes and modifications may be madetherein without departing from the scope of the invention as defined bythe appended claims.

What is claimed is:

1. An improvement in a cathode ray tube multibeam bipotential electrongun structure having a longitudinal axis therethrough and havingelectron generating means therein formed to emit a plurality ofseparately controlled electron beams whereof each beam emanates from asubstantially longitudinal arrangement of several related apertured gridelectrodes positioned in sequential orientation in front of a rearpositioned cathode component, said improvement being in the forwardregion of said electrode arrangement and comprising:

a common focusing electrode member having a forward oriented frontaperture plane spaced longitudinally from a rearward oriented rearaperture plane, said planes having a similar plurality of substantiallycircular related apertures therein, each of said front apertures havinga defined tube-like extensive encompassing member of substantiallycylindrical shaping integral with said front aperture plane andfabricated to extend rearward therefrom toward a relatedsmaller-dimensioned rear aperture formed in said rear aperture plane toeffect shielding for the respective electron beam passing there through;each of said tube-like shielding members being of substantially equalcross-sectional dimensioning and having a length at least equaling 50percent of the radius of the associated front aperture; and

a common accelerating electrode member positioned forward of saidfocusing electrode member and having an aperture plane proximal to thefront aperture plane of said focusing electrode member, saidaccelerating electrode aperture plane having a plurality of aperturestherein substantially mating in a spatial manner with the front orientedaper tures of said focusing electrode member, at least two of saidaccelerating electrode apertures being eccentrically aligned relative tosaid related focusing electrode front apertures to form nonsymmetricalelectrostatic lenses for focusing the respective individual electronbeams traversing the particular region; each of said focusing electrodeshielding members providing enhanced beam focusing by effecting improvedsymmetry of the equipotential lines of force in particularly the regionof low beam velocity in the focusing electrode portion of saidelectrostatic lensing field.

2. The multibeam electron gun improvement according to claim 1 whereinsaid gun structure is a three beam delta arrangement whereof the relatedelectrode components for each of the respective beams are positioned ina substantially equal off-axis orientation.

3. A multibeam electron gun improvement according to claim 1 whereinsaid plural beam gun structure is a three beam inline arrangementwhereof the related electrode components for the respective beams arepositioned in a manner to provide a center on-axis beam with relatedbeams equi-spaced on either side thereof, and whereof at least theside-related electrode arrangements include focusing electrode tubelikeshielding members of substantially equal lengths.

4. An improvement in a cathode ray tube employing a multibeambipotential electron gun structure whereof the individual plural beamsare directed to selectively impinge a patterned cathodoluminescentscreen discretely spaced therefrom, said improvement being in themultibeam electron gun structure wherein each of the respective beamsemanates from a substantially longitudinal arrangement of severalrelated apertured grid electrodes positioned in sequential orientationin front of a rear positioned related cathode component, said tubeimprovement being in the forward region of said electrode arrangementand comprising:

a common electrode member having a forward oriented front aperture planespaced longitudinally from a rearward oriented rear aperture plane, saidplanes having a similar plurality of related apertures therein, each ofsaid front apertures having a defined tube-like encompassing member ofsubstantially cylindrical shaping integral with said front apertureplane and fabricated to extend rearward therefrom toward a relatedsmallerdimensioned rear aperture formed in said rear aperture plane, andhaving a length at least equalling 50 percent of the radius of theassociated front aperture to effect shielding for the respectiveelectron beam passing therethrough; and

a common accelerating electrode member positioned forward of saidfocusing electrode member and having an aperture plane proximal to thefront aperture plane of said focusing electrode member, saidaccelerating electrode aperture plane having a plurality of aperturestherein substantially mating in a spatial manner with the front orientedapertures of said focusing electrode member, at least two of saidaccelerating electrode apertures being eccentrically aligned relative torelated focusing electrode front apertures to form non-symmetricalelectrostatic lenses for focusing the respective electron beamstraversing the particular region; each of said focusing electrodeshielding members providing enhanced beam spot focusing on said screenby effecting improved control of the equipotential lines of force inparticularly the region of low beam velocity in the focusing electrodeportion of said electrostatic lensing field.

1. An improvement in a cathode ray tube multibeam bipotential electrongun structure having a longitudinal axis therethrough and havingelectron generating means therein formed to emit a plurality ofseparately controlled electron beams whereof each beam emanates from asubstantially longitudinal arrangement of several related apertured gridelectrodes positioned in sequential orientation in front of a rearpositioned cathode component, said improvement being in the forwardregion of said electrode arrangement and comprising: a common focusingelectrode member having a forward oriented front aperture plane spacedlongitudinally from a rearward oriented rear aperture plane, said planeshaving a similar plurality of substantially circular related aperturestherein, each of said front apertures having a defined tube-likeextensive encompassing member of substantially cylindrical shapingintegral with said front aperture plane and fabricated to extendrearward therefron a related smaller-dimensioned rear aperture formed insaid rear aperture plane To effect shielding for the respective electronbeam passing therethrough; each of said tube-like shielding membersbeing of substantially equal cross-sectional dimensioning and having alength at least equaling 50 percent of the radius of the associatedfront aperture; and a common accelerating electrode member positionedforward of said focusing electrode member and having an aperture planeproximal to the front aperture plane of said focusing electrode member,said accelerating electrode aperture plane having a plurality ofapertures therein substantially mating in a spatial manner with thefront oriented apertures of said focusing electrode member, at least twoof said accelerating electrode apertures being eccentrically alignedrelative to said related focusing electrode front apertures to formnonsymmetrical electrostatic lenses for focusing the respectiveindividual electron beams traversing the particular region; each of saidfocusing electrode shielding members providing enhanced beam focusing byeffecting improved symmetry of the equipotential lines of force inparticularly the region of low beam velocity in the focusing electrodeportion of said electrostatic lensing field.
 2. The multibeam electrongun improvement according to claim 1 wherein said gun structure is athree beam delta arrangement whereof the related electrode componentsfor each of the respective beams are positioned in a substantially equaloff-axis orientation.
 3. A multibeam electron gun improvement accordingto claim 1 wherein said plural beam gun structure is a three beam inlinearrangement whereof the related electrode components for the respectivebeams are positioned in a manner to provide a center on-axis beam withrelated beams equi-spaced on either side thereof, and whereof at leastthe side-related electrode arrangements include focusing electrodetube-like shielding members of substantially equal lengths.
 4. Animprovement in a cathode ray tube employing a multibeam bipotentialelectron gun structure whereof the individual plural beams are directedto selectively impinge a patterned cathodoluminescent screen discretelyspaced therefrom, said improvement being in the multibeam electron gunstructure wherein each of the respective beams emanates from asubstantially longitudinal arrangement of several related apertured gridelectrodes positioned in sequential orientation in front of a rearpositioned related cathode component, said tube improvement being in theforward region of said electrode arrangement and comprising: a commonelectrode member having a forward oriented front aperture plane spacedlongitudinally from a rearward oriented rear aperture plane, said planeshaving a similar plurality of related apertures therein, each of saidfront apertures having a defined tube-like encompassing member ofsubstantially cylindrical shaping integral with said front apertureplane and fabricated to extend rearward therefrom toward a relatedsmaller-dimensioned rear aperture formed in said rear aperture plane,and having a length at least equalling 50 percent of the radius of theassociated front aperture to effect shielding for the respectiveelectron beam passing therethrough; and a common accelerating electrodemember positioned forward of said focusing electrode member and havingan aperture plane proximal to the front aperture plane of said focusingelectrode member, said accelerating electrode aperture plane having aplurality of apertures therein substantially mating in a spatial mannerwith the front oriented apertures of said focusing electrode member, atleast two of said accelerating electrode apertures being eccentricallyaligned relative to related focusing electrode front apertures to formnon-symmetrical electrostatic lenses for focusing the respectiveelectron beams traversing the particular region; each of said focusingelectrode shielding members providing enhanced beam spot focusing onsaid screen by effecting improved control of the equIpotential lines offorce in particularly the region of low beam velocity in the focusingelectrode portion of said electrostatic lensing field.